- Books Name
- CBSE Class 7 Science Book
- Param Publication
- CBSE Class 7
(c) Magnetic effect of electric current
According to Hans Christian Orested, magnetic effects are associated with current. It means, when electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current.
(i) Magnetic field
Let us take a card board tray through which a straight wire is passed in which current is passed. If some iron fillings are kept on to the card-board, it will arrange itself in concentric circles around the wire. Which shows that magnetic field is developed, when current is flowing in the wire.
In the same way, when a compass needle is placed below a current carrying conductor it deflects in a specific direction and if the direction of current changes, the direction of deflection in the compass needle also changes. That means a moving magnet can generate an electric current. Also we can say that electric current can produce a magnetic effect.
5. To show magnetic effect of electric current :
• Take a small piece of cardboard, make two holes and pass a wire through them.
• Now put a magnetic compass under the wire and rotate the cardboard till the needle of the compass comes parallel to the wire as shown in figure (a).
• Now connect the two free ends of the wire to the two terminals of a cell as shown in figure (b).
• Note your observation. Is there any deflection in the compass needle?
• Now change the connections of the wire with the cell by reversing the terminals and observe the direction of deflection. What happens when you disconnect or break the circuit?
The compass needle shows deflection when connected to the cell. This deflection gets reversed when the connection is reversed. There is no deflection upon disconnection.
The experiment shows that when electric current is passed through a conducting wire, it behaves like a magnet.
6. To show that a magnetic field is Introduced via electric current :
You have already seen in Activity , that the compass needle deflects on passing electric current through the wire. Now loop a long wire around the compass several times as shown in figure and pass the electric current.
You will see stronger deflection in the compass needle.
The needle of the compass shows higher deflection because of the increase in number of rounds of wire around the compass.
7. To show that the intensity/magnitude of the magnetic field increases with the increase in current intensity.
Use the arrangement of the earlier activity and connect the conducting wires to a battery of three cells of
1.5 Veach as shown in figure. Do you observe any change in the deflection of compass needle? Why?
The enhanced deflection in the compass needle is due to increase in the current density available through a battery of these cells of 1.5 Veach.